pcntl_waitpid

(PHP 4 >= 4.1.0, PHP 5)

pcntl_waitpid — Waits on or returns the status of a forked child

Description

intpcntl_waitpid
( int$pid
, int&$status
[, int$options = 0
] )

Suspends execution of the current process until a child as specified by
the pid argument has exited, or until a signal is
delivered whose action is to terminate the current process or to call a
signal handling function.

If a child as requested by pid has already exited
by the time of the call (a so-called "zombie" process), the function
returns immediately. Any system resources used by the child are freed.
Please see your system's waitpid(2) man page for specific details as to
how waitpid works on your system.

Parameters

pid

The value of pid can be one of the following:

possible values for pid

< -1

wait for any child process whose process group ID is equal to
the absolute value of pid.

-1

wait for any child process; this is the same behaviour that
the wait function exhibits.

0

wait for any child process whose process group ID is equal to
that of the calling process.

> 0

wait for the child whose process ID is equal to the value of
pid.

Note:

Specifying -1 as the pid is
equivalent to the functionality pcntl_wait() provides
(minus options).

please note, if you using configure option --enable-sigchild(Enable PHP's own SIGCHLD handler) when complie php(under linux 2.6.18-53.1.13.el5.centos.plus and php 5.2.5 as I know), pcntl_waitpid and pcntl_wait in php script would never return the child pid, because the build in handle get it first.